attach method
Implementation
void attach(OutputSource<O> box) {
box.listen((output) {
if (output is AsyncData<O>) {
if (output.value == null) {
store.delete(key);
} else {
store.write(key, codec.encode(output.value));
}
} else if (output is SyncOutput<O>) {
if (output.value == null) {
store.delete(key);
} else {
store.write(key, codec.encode(output.value));
}
}
});
}